1. Field of the Invention
The present invention relates to a method for controlling a power factor correction circuit, a controller for the power factor correction circuit, and a system for the power factor correction circuit.
2. Description of the Related Art
A power factor is a parameter for measuring a power efficiency of an electrical device, and a low power factor represents a low power efficiency. In electrical engineering, a power factor of an alternating current power system is defined as a ratio of an active power flowing into a load to an apparent power in a circuit, and it is a dimensionless number in the closed interval from −1 to 1. A power factor less than 1 means that a voltage waveform and a current waveform are out of phase, thus reducing an instantaneous product of the two waveforms. Actual power consumption is an ability of a circuit to execute operations at a specific time point. Apparent power is a product of a current and a voltage in the circuit. Since the energy is stored in the load and returned to a power supply, or the non-linear load distorts the waveform of the current drawn from the power supply, the apparent power is greater than the actual power. When a device (usually a load) generates power, a negative power factor is generated and flows to a generator which is generally regarded as a power supply. In an electrical power system, a load with a low power factor absorbs more current while transmitting a same useful power compared with a load with a high power factor. Higher currents increase energy losses in a power distribution system and require larger wires and other equipment. Due to the high cost of equipment and wasted energy, power companies typically charge higher costs to industrial or commercial customers with lower power factors.
Power Factor Correction (PFC) is a technique to increase the power factor of the electrical device. Linear loads (e.g., induction motors) with low power factors may be corrected through a passive capacitor or an inductive network. A nonlinear load (e.g., a rectifier) may distort the current drawn from the system. In this case, active or passive power factor correction may be configured to cancel distortion and increase the power factor. The device used to correct the power factor may be disposed in a central substation, distributed in a power distribution system, or provided in power consuming equipment.
However, current nonlinear PID (proportion, integral, differential) control is only able to handle a small range of input voltages and impedances. When an input voltage of the AC (alternating current) power source is high or the impedance range is wide, it is easy to cause an oscillation to the input current and the input voltage.
At present, there are complex equations to calculate the control parameters, and the calculated control parameters are configured to control a PFC circuit. These methods may solve most of the related oscillation problems. However, the problems of serious harmonic distortion and insufficient phase margin of the input current still remain unsolved.